The present invention generally concerns seeding techniques for growing diamond films, and articles and apparatus related thereto. More particularly, the present invention concerns methods for applying diamond particles to surfaces in ways facilitating growth of diamond films and/or diamond film patterns on planar and non-planar non-diamond surfaces, and articles and apparatus related to same.
Diamond films are particularly useful for wear resistant coatings since diamond is one of the hardest materials known to mankind. Advantageously, diamond also has a very high thermal conductivity, a large band gap, and excellent chemical/radiation resistance, thus also making the diamond films useful in high temperature and/or chemically and radiation active environments. Still further, pure diamond films are normally electrically insulative, but can be made electrically conductive by doping, thus making them useful in the electronic industry. For example, one particular application area is diamond film microsensors for sensing strain and temperature. With the advent of recent advances in chemical vapor deposition (CVD) processes, diamond films can now be grown on non-diamond substrates using CH.sub.4 and H.sub.2 in a timely and cost effective manner.
More particularly, one process of growing a diamond film includes dispensing diamond particles on the surface to be covered (i.e. "seeding") followed by a chemical vapor deposition (CVD) process utilizing CH.sub.4 and H.sub.2 in which the diamond particles are grown into a layer of crystalline diamond film. The CVD process is well known in the art and is explained, for example, in U.S. Pat. No. 4,925,701. However, the CVD process is very sensitive to the uniformity of the distribution of diamond particles. A non-uniform distribution of diamond particles results in undesirable diamond film characteristics such as thick and fifth areas, film roughness, and discontinuities and breaks in the film.
In U.S. Pat. No. 4,925,701, diamond particles are mixed with an aliphatic alcohol including isopropanol by use of a microsonic disrupter/agitator for achieving maximum uniformity of the suspension. The resulting suspension is applied to a surface by spin, spray or dip coating. However, as noted in a later U.S. Pat. No. 5,204,210, subsequent treatment or pretreatment by a photoresist or a comparable material/process is required in order to create diamond film patterns. Further, the process of patterning requires extra steps and additional manufacturing processing.
Recently, a mixture was made by adding diamond particles of about 0.1 microns average size to photoresist. The mixture was then applied to a flat surface of a substrate by spin coating to uniformly and evenly spread the diamond particles over the flat surface. This process had the advantage of reducing the number of steps required to seed a flat surface since the particles are applied simultaneously with the photoresist. However, the spin coating process is limited to a flat surface and cannot be selectively applied in a pattern without subsequent photolithographic steps. Further, the spin coating process requires the mechanical step of spinning the substrate. Also, the diamond particles of 0.1 microns tend to agglomerate and/or settle out of the photoresist mixture, thus requiring that the mixture be applied soon after mixing. Further, because of the relatively large size of the diamond particles, the 0.1 micron diamond particle mixture results in low nucleation densities and rough film surfaces. Still further, the CVD process grown diamond film exhibits poor adhesion strength when applied to non-diamond substrates, which undesirably limits the lifetime of the diamond film in many applications.
Thus, further advances are desired in terms of simplifying the manufacturing process such as by reducing the number of steps necessary to manufacture diamond film patterns. Also, advances in the application processes for seeding are desired so that non-planar surfaces can be more easily seeded for growing diamond films. Further, improvements are desired in methods and processes to make the processes less sensitive to agglomeration and to settling of diamond particles in a carrier. Further, it is desirable to improve the overall reliability and quality control of the seeding process. For CVD applications in microsensors and other electronic devices, smoother film surfaces are desirable. Also, improvements in the applicators and methods for applying diamond-particle-laden carriers are desired. Still further, improvements in the adhesion of the diamond films to substrates are desired. Concurrently, improvements in application apparatus, processes, materials, and synergistic combinations of same are desired.